Air pump capable of inflating an inflatable object regardless of air pressure level in the inflatable object

Abstract

An air pump is provided with a head, a cylinder, a valve chamber, a branch duct, an air discharging hole, and an elastic member. The cylinder comprises a first air chamber, and a second air chamber smaller in the cross-sectional area than the first air chamber. When air pressure in an inflatable object being inflated by the air pump has reached a certain pressure level, a displacement member of the valve member is caused to displace so as to allow the air in the first air chamber to be released into the atmosphere via the branch duct and the air discharging hole. In the meantime, the pumping action is automatically switched to the second air chamber through which air is continuously pumped into the inflatable object.

What is claimed is: 
     
       1. An air pump comprising: a head provided with a receiving cell and an air nozzle joint located in said receiving cell;   a first air chamber in communication with said receiving cell;   a second air chamber in communication with said receiving cell;   a valve chamber including at one end thereof a pressure hole communicating with the receiving cell;   a displacement member slidably located in said valve chamber, said displacement member including an air guiding portion;   an elastic element urging said displacement member toward said pressure hole;   a branch duct communicating between said first air chamber and said valve chamber; and   an air releasing hole communicating between said valve chamber and atmosphere;   wherein said air guiding portion is adapted to communicate between the branch duct and the air releasing hole;   whereby pressure in the receiving cell controls a position of the displacement member and selectively couples the first air chamber with the atmosphere.   
     
     
       2. The air pump as defined in claim 1, wherein said displacement member is provided with two leakproof rings, one of said two leakproof rings being located between said pressure hole and an opening of said branch duct, another one of said two leakproof rings being located between said branch duct and said air releasing hole when said displacement member is contiguous to said pressure hole; and wherein said air guiding portion of said displacement member is located between said two leakproof rings. 
     
     
       3. The air pump as defined in claim 1, wherein said head is further provided with a bolt fastened with an open end of said valve chamber such that said bolt is urged by one end of said elastic element, said elastic element including another end urging said displacement member. 
     
     
       4. The air pump as defined in claim 3, wherein said bolt has a knob which is located outside said valve chamber. 
     
     
       5. The air pump as defined in claim 1, wherein the pressure hole is in communication with said receiving cell of said head and said valve chamber. 
     
     
       6. The air pump as defined in claim 1, wherein air from the first chamber flows transversely across the air guiding portion. 
     
     
       7. In an air pump for an inflatable object, the pump being of the type including a first low-pressure air chamber,   a second high-pressure air chamber, and   an air receiving cell communicating with an air nozzle adapted to be coupled in communication with the inflatable object; the improvement comprising: a valve responsive to pressure in the air receiving cell, the valve adapted to leak air from the low-pressure air chamber to atmosphere when the pressure in the air receiving cell reaches a certain level;   whereby air inflating action is automatically switched to the high-pressure air chamber.     
     
     
       8. The improvement according to claim 7, wherein the first low-pressure air chamber further comprises a low-pressure piston slidable within a low-pressure cylinder, wherein the second high-pressure air chamber further comprises a high-pressure piston slidable within a high-pressure cylinder, and wherein the second high-pressure air chamber is movable relative to the first low-pressure air chamber in a direction of an axis thereof. 
     
     
       9. The improvement according to claim 7, comprising a check valve between the air receiving cell and the first low-pressure air chamber.